1. Field of the Invention
The present invention relates to a demist controller for controlling the demist operation of an automobile air-conditioner for removing the mist from a window glass of an automobile or preventing formation of a mist on the window glass.
2. Description of the Prior Art
There are known demist controllers incorporated in automobile air-conditioners for removing the mist from a window glass of an automobile or preventing collection of a mist on the window glass. The known demist controllers include a humidity sensor for directly detecting the humidity in the vicinity of the inside surface of a window glass. The detected humidity is compared with reference values or criteria for automatically controlling starting and stopping of the demist operation of an automobile air-conditioner. Since the humidity sensor changes its impedance characteristics and capacitive characteristics as the time goes on, a correction of the criterion is necessary when the humidity sensor is used throughout the service life of the automobile.
To this end, a separate manual adjustment means is provided for manually changing the criteria for starting and stopping the demist operation of the air-conditioner, as shown in Japanese Patent Laid-open Publication No. 62-194929, for example.
In order to maintain a properly controlled demist operation for a long period of time, the manual adjustment means must be actuated periodically by a driver, a dealer or a manufacture for adjusting the criteria. Such frequent actuation of the adjustment means is tedious and time-consuming.